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Views Hierarchy

Introduction

In iOS, a view object means anything that is capable of drawing itself in a rectangular region on an iOS screen.

For example, a label is a view object, and a button is another view object.

When you are looking at the user interface of any random iOS application, that one screen might contain 5, 10 or maybe more than 20 different view objects.

Some views are large, and some are tiny. Some views might show an image, and some might display text, some might show both.

Let's back in the code for the FirstApp project. In ViewController.swift file we are using a view to change the background color.

This view is an object that already exists as part of the storyboard.

It is not referring to any of the view objects we have added, because when you create a new Xcode project, and you will also get that first storyboard.

It included the outline of a single screen, and it is simply called view.

Now we might describe this as empty, but it is not, because it is a view object configured to draw itself and to fill all available screen size on whatever device it runs on.

So in our FirstApp project, all these labels, and a button are all independent view objects.

They are currently all nested inside this larger generic view object, and you can see them in Document Outline.

So as this is our top-level view object, all these labels and this button are inside it, so they are all subviews of the top-level view. This idea of views with subviews inside them is useful because in the code we could ask this top-level view to give all of its subviews.